Search PubMed⌕ Search

Biomedical subjects

M Leijon

Publications and source records attributed to M Leijon.

At least 19 recordsLinked to original sources

Adding functional entities to plasmids.

Non-viral gene therapy constitutes an alternative to the more common use of viral-mediated gene transfer. Most gene transfer methods using naked DNA are based upon non-sequence-specific interactions between the nucleic acid and cationic lipids (lipoplex) or polymers (polyplex). We have developed a technology in which functional entities hybridize in a sequence-specific manner to the nucleic acid (bioplex). This technology is still in its infancy, but has the potential to become a useful tool, since it allows the construction of highly defined complexes containing a variety of functional entities. In its present form the bioplex technology is based upon the use of peptide/nucleic acids (PNA) as anchors. Single, or multiple, functional entities are directly coupled to the anchors. By designing plasmids, or oligonucleotides, with the corresponding anchor target sequence, complexes with desired composition can easily be generated. The long-term aim is to combine functional entities in order to achieve optimal, synergistic interactions allowing enhanced gene transfer in vivo.

Cell Nucleus↗

Imino proton exchange in DNA catalyzed by ammonia and trimethylamine: evidence for a secondary long-lived open state of the base pair.

The base-pair opening kinetics of the self-complementary oligomer d(CGCGAATTCGCG)(2) has been derived from NMR measurements of the imino proton exchange. In general, it has previously been found that imino proton exchange in duplex DNA is limited by the proton-transfer step from the open state and that the dependence of the exchange times on the inverse concentration of an added exchange catalyst is linear. In the present study, a curvature is observed for, in particular, the innermost AT base pair with both ammonia and trimethylamine (TMA) as exchange catalysts. The two catalysts act on the same open states, but the accessibility of TMA is reduced by a factor of 2-3 compared to ammonia. Assuming that ammonia accesses the imino proton equally in the open state of the base pair and in the mononucleoside, the curvature is consistent with 7-9% of the openings ending in open states with lifetimes of about 1 micros while the bulk of open-state lifetimes fall in the nanosecond range. A curvature is also found for the exchange times of the imino protons in the A-tract sequence CGCA(8)CGC/GCGT(8)GCG. This curvature becomes increasingly pronounced from the 5'-end toward the center of the tract and hereby seems to be correlated with the contraction of the minor groove. Thus, while the base-pair lifetimes deduced from the present study are in accordance with previous measurements, a substantial fraction of the open states formed by the central AT-base pairs in the two oligomers exhibits microsecond lifetimes in contrast to previous estimates in the nanosecond range. These findings may be of relevance for the way sequence specific recognition is accomplished by proteins and ligands.

Ammonia↗

High base pair opening rates in tracts of GC base pairs.

Sequence-dependent structural features of the DNA double helix have a strong influence on the base pair opening dynamics. Here we report a detailed study of the kinetics of base pair breathing in tracts of GC base pairs in DNA duplexes derived from 1H NMR measurements of the imino proton exchange rates upon titration with the exchange catalyst ammonia. In the limit of infinite exchange catalyst concentration, the exchange times of the guanine imino protons of the GC tracts extrapolate to much shorter base pair lifetimes than commonly observed for isolated GC base pairs. The base pair lifetimes in the GC tracts are below 5 ms for almost all of the base pairs. The unusually rapid base pair opening dynamics of GC tracts are in striking contrast to the behavior of AT tracts, where very long base pair lifetimes are observed. The implication of these findings for the structural principles governing spontaneous helix opening as well as the DNA-binding specificity of the cytosine-5-methyltransferases, where flipping of the cytosine base has been observed, are discussed.

Base Pairing↗

Gender trends in sick-listing with musculoskeletal symptoms in a Swedish county during a period of rapid increase in sickness absence.

UNLABELLED: Sickness absence and disability pension due to musculoskeletal diagnoses has increased in Sweden. STUDY OBJECTIVE: To study gender trends in sickness absence with musculoskeletal diagnoses and its changes in 1985-87. DESIGN: A prospective population-based study of all new sick-leave spells exceeding seven days in 1985-87. Sickness absence with "all diagnoses" was compared to "all musculoskeletal diagnoses", the latter group was also divided into three sub-groups. SETTING: The county of Ostergötland, Sweden. PARTICIPANTS: All sick-leave insured aged 16-65; 107,000 women and 100,000 men. RESULTS: More women than men were sick-listed in "all diagnoses" in 1985. There were corresponding gender differences in sickness absence with musculoskeletal diagnoses except with the diagnosis "low back pain". Sick-listing with musculoskeletal diagnoses increased for both women and men from 1985 to 1987, but the increase was consistently much higher for women, especially for younger women.

Absenteeism↗

Unique base-pair breathing dynamics in PNA-DNA hybrids.

Kinetic and thermodynamic parameters, derived from 1H-NMR measurements of the imino proton exchange rates upon titration with the exchange catalyst ammonia, are reported for two mixed-sequence peptide nucleic acid (PNA)-DNA hybrids and their counterpart DNA duplex. The exchange times of the imino protons in the PNA strands extrapolate to very short base-pair lifetimes in the limit of infinite exchange catalyst concentration. This is not due to generally less stable base-pairs in PNA-DNA hybrids, since the lifetimes, apparent dissociation constants and thermodynamic stability (DeltaG degrees ) of the innermost DNA guanine imino protons are similar in the hybrid duplexes and in the DNA duplex. In addition, the apparent dissociation constants determined for PNA bases of the hybrids are of the same order as those of the corresponding bases in the DNA duplex. An exchange process from the closed state was found to be inconsistent with the experimental data. From these results, we conclude that opening and closing rates of the PNA guanine and thymine bases are at least two orders of magnitude higher than those of the corresponding bases in the DNA duplex. Unusual kinetics in the hybrids is also evident from the destabilization of the complementary DNA strand thymine bases, which exhibit base-pair dissociation constants increased by approximately two orders of magnitude compared to what is observed in the DNA duplex, while the DNA strand guanine bases are largely unaffected. The general pattern of the base-pair dynamics in the hybrids obtained when using trimethylamine as an exchange catalyst is the same as when using ammonia. However, the long base-pair lifetimes i. e. those of the DNA duplex and the guanine bases of the DNA strands in the hybrids, are approximately three to five times longer than when using ammonia. Thus, all opening events sensed by ammonia are not accessible to trimethylamine. These observations are discussed in regard to the mechanism of base-pair opening and the nature of the open state.

Ammonia↗

Internal motions of nucleic acid structures and the determination of base-pair lifetimes.

Over the years, imino proton exchange measurements have provided a description of base-pair opening and of properties of internal motions of nucleic acids such as the individual opening of base pairs and the insensitivity of base-pair lifetimes to the nature and stability of neighboring pairs. A recent determination of base-pair lifetimes in d(CGCGATCGCG) conflicts with the original measurements and their interpretation. This question is analyzed in the present work. We emphasize the importance of high concentrations of exchange catalyst (eg 1 M NH3) for the accurate determination of base-pair lifetimes. These concentrations entail a high ionic strength, which can lead to aggregation, enhanced magnetic relaxation and underestimation of base-pair lifetimes if exchange is measured by its effect on the proton relaxation rate. Magnetization transfer which provides a more direct method for the measurement of proton exchange rates is therefore preferred. We show that the lack of measurements at high catalyst concentration is responsible for the discrepancy mentioned above. Measurements by the magnetization transfer method validate the original interpretation and inversion recovery experiments illustrate the effect of the ionic strength on the relaxation rate of the imino protons.

Base Composition↗

Long-term economic effects of team-based clinical case management of patients with chronic minor disease and long-term absence from working life.

OBJECTIVES: To examine the socio-economic effects of team-based clinical case management of patients with chronic minor disease bound for early retirement. DESIGN: Marginal analysis of programme costs and benefits to society compared with no-programme baseline of costs occurring in society due to productivity loss. Prospective patient data collection on admission, discharge, and at one year and five years after discharge to determine programme effectiveness. SETTING: Out-patient clinic at the department of social medicine in tertiary care hospital. SUBJECTS: 239 patients with minor disease and long-term vocational absence consecutively admitted to the study. At the one-year evaluation, 17 patients had been readmitted to the team, 7 could not be found, 6 declined the interview and 2 were deceased. At the five-year evaluation of 49 patients who were active after one year, one was deceased and 10 were unable to be found. MAIN OUTCOME MEASURES: Vocational activity. Programme costs. Benefits to society measured by decrease in indirect costs. RESULTS: The one-year vocational rehabilitation rate from the program was 20.5% and the five-year rehabilitation rate was 11.3%. The total discounted cost for case management of the 239 patients was 7.3 MSEK (600,000 Pounds). The decrease in the indirect costs to society from the 28 patients found active after five years was 35.1 MSEK (2,500,000 Pounds). The net present value of the programme at the 1991 price level was 27.5 MSEK (2,365,000 Pounds). CONCLUSIONS: Tertiary care level team-based clinical case management for vocational rehabilitation of patients with chronic minor disease has a positive cost-benefit ratio. A cross-boundary awareness at a health policy level is needed of the societal costs involved for this group of patients who fall between the traditional services in health care and social work.

Absenteeism↗

Proton exchange rates measured by saturation transfer using delayed randomization of the solvent magnetization.

The spin-lock saturation transfer experiment introduced by B. Adams and L. Lerner (J. Magn. Reson. 96, 604-607, 1992) is analyzed in terms of the Bloch equations. It is shown that the T1rho relaxation of the solvent is introduced in the decay of the exchangeable protons under conditions of relatively rapid exchange. An alternative experiment is suggested that randomizes the solvent magnetization with a pulsed field gradient before the observe pulse. This gives a single exponential intensity decay for the exchanging protons at all exchange rates. In addition, efficient water suppression and an even excitation profile are obtained.

DNA↗

Sex differences in sickness absence in relation to parental status.

The aim of this study was to analyse sex differences in medically certified sickness absence with special regard to parental status and age. All new sick-leave spells exceeding seven days and certified by a physician in a county of Sweden were registered in 1985-1987. The data-base was related to the population at risk by using data from the Swedish Official Population and Housing Census 1985. The analysis concerned the employed population in the age group from 16 to 54 with and without custody of children younger than ten years. In all ages, women with children had more sickness absence than men with children. Corresponding sex differences did not appear for persons without children, except for the oldest age-groups. Men with children had the lowest sickness absence of all groups. Young women with children had the highest. These findings remained the same when pregnancy-related sickness absence was excluded. The common finding of sex differences in sickness absence is here highly interrelated to custody of small children. The results suggest that the often reported positive health effects of multiple roles in women may be counteracted by inequality between the sexes in the responsibility as parents.

Absenteeism↗

NMR studies and restrained-molecular-dynamics calculations of a long A+T-rich stretch in DNA. Effects of phosphate charge and solvent approximations.

The nonamer duplex d(GCAAAAACG).d(CGTTTTTGC) was studied by 1H-NMR at 500 MHz. With the exception of the H5' and H5" sugar protons, all protons were assigned by two-dimensional NMR experiments [NOE spectroscopy (NOESY), double-quantum-filtered J-correlated spectroscopy (DQF-COSY) and total correlation spectroscopy (TOCSY)]. The exchange kinetics of the imino protons of the Watson-Crick base pairing were studied at 15 degrees C by measuring inversion-recovery rates under conditions of extensive ammonia base catalysis. Extrapolation to infinite base concentration gave anomalous long lifetimes for the A-tract in accordance with previous results [Leroy, J.-L., Charettier, E., Kochoyan, M. & Guéron, M. (1988) Biochemistry 27, 8894-8898]. On average, 11 NOESY distance constraints/nucleotide were evaluated using the complete relaxation matrix approach. Deoxyribose coupling constants were obtained from simulations of the DQF-COSY cross-peaks, assuming a rapid two-state equilibrium between a C2'-endo and C3'-endo conformer. The sugars were found to be predominantly in the C2'-endo conformation. The NMR-derived distance and torsion constraints were implemented into three different restrained-molecular-dynamics (rMD) protocols, two in vacuo, with different charges on the phosphate group and the third with the solvent explicitly included. All protocols displayed good convergence from different starting structures. The structures derived from the three protocols satisfied experimental restraints equally well and had similar final energies. Although the overall pattern of sequence dependence of helical parameters shows some resemblance in all structures, we find that the absolute amplitudes of the parameters are largely dependent on the rMD protocols, particularly the twist parameters. The minor groove distance P(n + 2)-P(m + 2) varies from 0.7 nm to 1.2 nm in the three protocols. Still the NOESY-derived anomalously short distances AH2(n)-H1'(m + 1) and AH2(n)-H1'(n + 1), n and m denote complementary residues, which are assumed to be indicative of a compressed minor groove, are kept in all calculated structures.

Base Composition↗

Structural characterization of PNA-DNA duplexes by NMR. Evidence for DNA in a B-like conformation.

The nucleic acid analogues PNA (peptide nucleic acids) hybridize with DNA of complementary sequence. The solution structures of two PNA-DNA duplexes, H-(GCTATGTC)-NH2.d(GACATAGC) and H-(GTAGATCACT)-NH2.d(AGTGATCTAC), have been studied by 1H NMR. It was found that the PNA-DNA hybrids are base paired by hydrogen bonds, most likely of the Watson-Crick type. From two-dimensional NOESY and COSY results it is concluded that the DNA strand in the PNA-DNA complex adopts a B-like structure with the deoxyribose sugars in the C2'-endo conformation.

Base Composition↗

Binding of delta- and lambda-[Ru(phen)3]2+ to [d(CGCGATCGCG)]2 studied by NMR.

The interactions of the delta and lambda enantiomers of the chiral metal complex [Ru(phen)3]2+ (phen = 1,10-phenanthroline) with the oligonucleotide duplex [d(CGCGATCGCG)]2 have been studied with NMR and CD spectroscopy. From NOESY data it is shown that the interaction primarily takes place in the minor groove of the oligonucleotide which remains in a B-like conformation. The observed NOEs also provide evidence that the metal complexes preferentially bind to the central AT region. The observed AT specificity is more pronounced with the delta as compared to the lambda enantiomer, which interacts with a larger part of the oligonucleotide. Furthermore, the NOESY data show that neither of the enantiomers binds by classical intercalation. This is also supported by a comparison study of the analogue [Ru(phen)2DPPZ]2+ (DPPZ = dipyrido[3,2-a:2',3'c]phenazine) which intercalates in DNA. The NMR as well as the CD results show that the delta and lambea enantiomers of [Ru(phen)3]2+ bind in different modes to [d(CGCGATCGCG)]2. Comparison of CD spectra of the metal complex in the presence of [d(CGCGATCGCG)]2, poly(dAdT).poly-(dAdT), poly(dGdC).poly(dGdC), and calf thymus DNA suggests that these binding modes are independent of DNA sequence. The results are found to be compatible with binding of delta-[Ru(phen)3]2+ by insertion of two phenanthroline ligands into the minor groove, causing minor distortions of the DNA structure, whereas the lambda enantiomer binds in a mode that leaves the DNA structure unaffected.

Base Sequence↗

The interaction of ellipticine derivatives with nucleic acids studied by optical and 1H-nmr spectroscopy: effect of size of the heterocyclic ring system.

The DNA interaction of derivatives of ellipticine with heterocyclic ring systems with three, four, or five rings and a dimethylaminoethyl side chain was studied. Optical spectroscopy of drug complexes with calf thymus DNA, poly[(dA-dT).(dA-dT)], or poly[(dG-dC).(dG-dC)] showed a 10 nm bathochromic shift of the light absorption bands of the pentacyclic and tetracyclic compounds upon binding to the nucleic acids, which indicates binding by intercalation. For the tricyclic compound a smaller shift of 1-3 nm was observed upon binding to the nucleic acids. Flow linear dichroism studies show that the geometry of all complexes is consistent with intercalation of the ring system, except for the DNA and poly[(dG-dC).(dG-dC)] complexes of the tricyclic compound, where the average angle between the drug molecular plane and the DNA helix axis was found to be 65 degrees. One-dimensional 1H-nmr spectroscopy was used to study complexes between d(CGCGATCGCG)2 and the tricyclic and pentacyclic compounds. The results on the pentacyclic compound show nonselective broadening due to intermediate chemical exchange of most oligonucleotide resonances upon drug binding. The imino proton resonances are in slow chemical exchange, and new resonances with upfield shifts approaching 1 ppm appear upon drug binding, which supports intercalative binding of the pentacyclic compound. The results on the tricyclic compound show more rapid binding kinetics and very selective broadening of resonances. The data suggest that the tricyclic compound is in an equilibrium between intercalation and minor groove binding, with a preference to bind close to the AT base pairs with the side chain residing in the minor groove.

Animals↗

Pregnancy related sickness absence in a Swedish county, 1985-87.

Sickness absence during pregnancy has increased in Sweden as well as in other countries. STUDY OBJECTIVE--The study aimed to describe pregnancy related sickness absence and its increase from 1985-87; to consider if the increase were parallel to an increase in sickness absence for all diagnoses or could be explained by a higher birth rate; and to compare different ways of presenting sickness absence data. DESIGN--The data from a prospective incidence study of all new sick leave spells exceeding seven days in 1985-87 were related to the population at risk through relevant data from different registers. SETTING--The county of Ostergötland, Sweden (about 400,000 inhabitants). PARTICIPANTS--Subjects were approximately 70,000 sick leave-insured women aged 16-44 years, of whom some 15,000 had sickness absences > seven days. Some 4600 women gave birth in 1985, approximately 1300 of whom were listed as having pregnancy related diagnoses. MAIN RESULTS--The number of women with sick leave associated with pregnancy related diagnoses increased by 24% (95% confidence interval (CI) 15, 33%) during the period. This diagnosis group was one of the very few with an increasing number of people listed as sick. The corresponding increase for all diagnoses in women aged 16-44 years was < 1% (95% CI 1, 3%). The increase in the number of women who gave birth was 9% (95% CI 5, 13%). The sick leave rate associated with pregnancy related disorders increased by 14% (95% CI 7, 21%) in 1985-87, while that in all women aged 16-44 years increased by 3% (95% 1, 5%). (p < 0.0001). The number of sick leave days associated with pregnancy related disorders increased by 49% (p < 0.0001) in the period--twice the equivalent increase (p < 0.0001) in the total number of sick leave days for all diagnoses taken together. The sick leave rate and duration, like the increase in these variables, varied with age. Different ways of presenting the length of absence proved complementary to each other. CONCLUSIONS--After correcting for changes in the overall sick leave rate and in the birth rate, there is still an 11% increase in the sick leave rate associated with pregnancy related disorders that needs to be explained. Medical factors cannot explain this increase but changes in attitudes and practice in relation to sickness insurance among pregnant women and their doctors merit further study.

Adolescent↗

Epidemiology of sickness absence in a Swedish county in 1985, 1986 and 1987. A three year longitudinal study with focus on gender, age and occupation.

In order to get a better epidemiological base for preventive intervention in the county of Ostergötland, Sweden, a comprehensive study of sickness absence was done. During the years 1985, 1986 and 1987, all new periods of sick-leave exceeding seven days were registered with demographic variables. This information was related to data about the total population of Ostergötland. Each year approx. 45,000 persons had approx. 61,000 sickness spells. These figures were stable over the years while the number of sick-leave days increased. Blue-collar occupations had the highest sick-leave rates and the female sick-leave rate was higher in general and much higher in most male-dominated occupations. The male rate was lower within female-dominated areas, except among secretaries and textile workers. Females in extremely male-dominated groups had the highest rates, while both male and female sick-leave rates were lower in more gender-integrated occupations.

Absenteeism↗

Effects of sequence and length on imino proton exchange and base pair opening kinetics in DNA oligonucleotide duplexes.

The base catalysed imino proton exchange in DNA oligonucleotides of different sequences and lengths was studied by 1H-NMR saturation recovery experiments. The self-complementary sequences studied were GCGCGAATTCGCGC (I), CGCGAATTCGCG (II), GCGAATTCGC (III), and CGCGATCGCG (IV). The evaluation of base pair lifetimes was made after correction for the measured 'absence of added catalyst' effect which was found to be characterized by recovery times of 400-500 ms for the AT base pairs and 250-300 ms for the GC base pairs at 15 degrees C. End effects with rapid exchange is noticeable up to 3 base pairs from either end of the duplexes. The inner hexamer cores GAATTC of sequences I-II show similar base pair lifetime patterns, around 30 ms for the innermost AT, 5-10 ms for the outer AT and 20-50 ms for the GC base pairs at 15 degrees C. The shorter sequences III and particularly IV show much shorter lifetimes in their central AT base pairs (11 ms and 1 ms, respectively).

Base Composition↗